Fan



May 19, -942. J. E. McDoNALD 2,283,609

FAN

Filed Nov. 8, 1959 l 2 shams-sheet` 2 i .yf

INVENTOR Joy/v E. McDoMJ-D BY @d il W ATTORNEY Patentecl May 19, 1942 uni rs Y srarrs recrear i oFF-ics FAN John E. McDonaldBoston, lv/Iass., assignor to B. F. Sturtevant Co ton, Mass.

Appli'cation November 8, 1939, Serial'No. 303,412-

` e claims. (o1. 2st- 114) This invention relates to Ymethods of and apparatus for controlling the volume of air, moved by fans.

An object of the invention is to utilize the socalled Magnus effect for varying and controlling the volume of air moved by fans.

Another and more definite object of the invention is to utilize so-c'alled Flettner`rotors in the inlet of a fan for varying' the spin velocity of the air entering the fan. y

As'discussed in the U. Sl. Patent No. 1,846,863

issued Feb. 23, 1932, on an application ofV H. F.

Hagen, it is desirable to operate a fan atconstant speed and to vary the volume of the air moved by the fan by varying the spin velocity of the air entering the fan, in the direction of rotation of the fan blades.

This invention utilizes rotors in a fan inlet, s0

positioned and so rotated about their axes, as to control the volume of air moved by the fan by varying the spin velocity of the air entering the fan, in thedirection of rotation of the fan blades.

In one embodiment of the invention, a plu# rality of rotors are mounted in the inletof a fan with their aXes converging towards the axis YofY the fan.

AE=ap(Cu2T2-CLL111) a=angular speed of the fan Wheel fr :air density C1t1=spin component of velocity of the air at th:

inlet side of the wheel Cu2,=spin component at the Vdisch-arge side of the Wheel r1=radius at the inlet side of the wheel y1i2=radiusat the discharge side of the wheel As disclosed in said'Hagen patent, the useful output of energy of a fan yat a constant angular speed, can be reducedA by making the term'Cum positive. Since in general, r1 the inlet radius of the fan blading is fixed, such variation in energy" l Voutput must be accomplished by a variation or" the term C'u1. In said Hagen patent, this variation is obtained through the use of adjustable vanes in the inlet of a fan.

A rotating cylinder instill air will induce about itself a circulatory airl motion of such nature In another embodiment of the invention, a

plurality of rotors are mounted with their axes substantially parallel, around the inlet of a fan.

In all embodiments of the invention, the volume of air moved by the fan is controlled. by varying the speed of rotation their axes.

The invention will now be described with-reference to the drawings,'of which:

Fig. 1 is a diagrammatic View illustrating thel action of an unconned rotor revolving at'low speed, upon air moving past it;

Fig. 2 is a diagrammatic view similar to Fig. 1 but illustrating the rotor revolving at a higher speed.

Fig. 3 is a diagrammatic but illustrating the rotor speed;

view similar to Fig. 2 revolving at ahigher Fig. 4 is a partial transverse section through al centrifugal fan embodying this invention;

Fig. 5 is a side view looking into thefeye of the fanofFig.4; if

Fig. 6 is a siderview of another embodiment of this invention applied to a centrifugal fan having an involute casing, and

Fig. 7 is a partial transverse section through the inlet box of the fan of Fig. 6.

In any fan, a simple measure of the energy added to each unit volume of air flowing through it, is theexpression of the rotors 'about varies conformably with increases in the rotative speed :ofthe cylinder.

When revolvable rotors of this type are located in the eye-'of a, fan as inustrated in one embodiment by Figs. 4 and 5 and as illustrated in -an- Y other embodiment by'Figs. 6 and 7, the air passing between the rotors will be given a spincomponent. The circulation in the 'air'stream behind the rotors'will be equal to the sum of the rotor circulations. Since it now seems desirable that.. circulation should be constant across the Ysection/of the vair leaving the rotors, it is preferred that the circulation about each rotor should be constant along its length, and that therefore'the-rotorsbe substantially cylindrical as illustrated.

The circulation about a rotor may be written Girculation=2TrRV where R=distance of any Vpoint in the air Y stream from therotor axis V=spin or tangential velocity of `the air at thereference point.-

If the reference point is on the surface of the cylinder, then Circulation=21rRoVo with Ro the radius of the rotor and Vo the tip speed of the rotor. But

Vo=21rRoS where S is the revolving speed of the 5 rotor.

Hence Y Circulation=41r2lRu2S If there are Z rotors in all, the total circulation behind the rotors will be Circulation=Z (41r2Ro2S Cul 21rd a (21rR02S) where a is the distance of the base of the blades of the fan wheel from its axis. The energy added to each unit volume of air will be The above formula has been used to calculateA the effect of four 3" radius rotors revolving at 1800 R. P. M. in the eye of a centrifugal fan having a wheel diameter of 34". Such a wheel may produce an air pressure of 5" of water with a Cuzrz of 130 in feet second units. The

l term Z(21rR02S) will then have a value of approximately 47, as is shown by the substitution of appropriate values.

` Cu2r2-Z 21rRo2S) :13G-47:83 and the air pressure with the rotors revolving at 1800 R. P. M. will be by proportion The pressure may be increased by slowing down the rotors. At zero R. P. M. the pressure will be 5". The reduction in pressure may be increased by revolving the rotors at higher speeds.

Due to the nature of air, tests have shown that the performance is notY that as mathematically demonstrated in the foregoing. To produce a given reaction, the rotor speeds should be from two to three timeshigher than the theoretical ones.

To provide more than a 40% reduction in air pressure, the vrotor speeds may be so high as to be impractical. But a 40% reduction in pressure results in more than a 50% saving in horsepower and it is now preferred where reductions in pressure of more than 40% are desired, that the further reduction be accomplished as in the past, by dampers.

Since the volume of the air delivered by thefan varies as the square root of the pressure produced, assuming fixed air resistance, changes in the pressure producing capacity of a fan are Vaccompanied by reductions in volume flow.

The cylindrical rotors I of Figs. 4 and 5 are arranged in the eye II of the centrifugal fan I2, with their axes extending substantially at right angles to the convergingV inlet member I3, and converging towards the axis of the fan wheel indicated generally by I4.

The rotors I0 are adapted to be rotated about their shafts I which are attached at their outer ends to the inlet member I3 by means of the plates I8 and the nuts I1 which are screwed onto the threaded ends of the shafts, against the plates. The inner ends of the shafts IIJ are screwed into tapped circular apertures in the casing of the electric motor IB.

The inner ends of the rotors I0 are attached to the gears I1 which rotate around the bearings I8 on the shafts I5. The outer ends of the rotors are attached to the bearings I9 which rotate around the shafts I5.

The armature of the motor I6 drives through its shaft 28, the gear 2l which meshes with the gears I8 to rotate them and through them the rotors I0 simultaneously and in the same direction.

' The stream lining fairing 22 is attached by the clips 23 to the motor I6 and serves to guide the air smoothly around the motor I6 and into the fan wheel I4. The motor I6, the rotor assemblies and the fairing are supported by the shafts I5 from the fan housing although external supports may be provided vif desired.

The fan wheel I4V consists of the blades 24 which are attached to the back plate 25 which in turn is attached to the stream lining hub 26 which is keyed onto the rotary shaft 21. The shaft 21 is supported from a, conventional bearing pedestal which is noty shown. Only two fan blades 24 are illustrated but more would be included in a wheel. For example eight blades could be provided.

The motor I6 is a variable speed electric motor and its speed may be controlled by a conventional controller.

In operation, the fan wheel I4 is driven at a constant speed and the rotors I0 are rotated about their shafts I5 at speeds to give the desired air volumes. If the rotors are not revolved while the fan wheel is rotated, they will have no eect upon the air volume. Their eiect when revolving about their axes will vary with their speed of rotation, and this eifect may be calculated from the formula andk other data given herein.

Figs. 6 and?? illustrate an application ofthe invention to a centrifugal fan of the type illustrated by said Hagen patent and which includes y. an involute casing. In this embodiment, the six rotors 30 have their shafts 3| rotatably supported in the bearings 32 which in turn are supported in the inlet walls 33. The uppermost rotor 30 has an extended shaft 3| on which is mounted an inner pulley 34 and an Outer pulley 35. 'Ihe other rotors 3D have shorter shafts 3l on which are mounted only the pulleys 34.

The variable speed electric motor 36 is mounted'on the casing 31 of the fan and has mounted on its shaft, the pulley 38 which is in alignment with the pulley 35. The belt 39 is fitted around the pulleys 35 and upon rotation of the pulley 38 by the motor 36, the pulley35 is rotated.

The inner pulleys 34 are in alignment and are Upon rotation of .the

tated and with them the rotors 30. The rotors 30 produce variable spin velocities in the airpassing between them conformably with their speedvformation. I

The speed of the electric motor 36 may be adjusted by a conventional controller to adjust the speed of the rotors'to provide the desired air volume.

Y An advantage ofthe use of rotors for adjusting the air volume is that no -throttling effect exists as in the case of vanes which have previously been used.

While embodiments of the invention have been described for the purpose of illustration, it should be understood that the invention is not limited to the exact apparatus and arrangements of apparatus described, as departures therefrom may be suggested by those skilled in the art without departure from the essence of the invention.

What is claimed is:

1. In a fan having a plurality of rotary, air moving blades and a stationary, air guiding casing forming an axial, air inlet to said blades, a plurality of rotors having shaft supporting means attached to said casing, said rotors being so disposed with respect tothe air stream flowing through said inlet that upon rotation thereof, they produce a spin velocity in the air in the direction of rotation of said blades, means independent of the air moved by said fan for rotating said rotors in the direction of the air movement produced in said inlet by the rotation of said blades, and means for adjusting said last mentioned means for varying the speed of rotation of said rotors for varying the volume of air moved by said fan.

2. In a fan having a plurality of rotary, air moving blades and a stationary, air guiding casing forming a converging air inlet to said blades in alignment with the axis thereof, a plurality of rotors having radial shafts, means attached to said casing for supporting said shafts, said rotors being so disposed with respect to the air stream iiowing through said inlet that upon rotation thereof, they produce a spin velocity in the air in the direction of rotation of said blades,

means independent of the air moved by said fan for rotating said rotors in the direction of the movement of the air by the rotation of said blades, and means for adjusting said last mentioned means for varying the speed of rotation of said rotors for varying the volume of air moved by said fan.

3. In a centrifugal fan having a wheel and a stationary, air guiding casing forming an axial, air inlet to said wheel, a plurality of rotors having spaced shafts, means attached to said casing around said inletl for supporting said shafts, said shafts being substantially parallel to the axis of said Wheel, said rotors being so disposed with respect to the air stream flowing through said inlet that upon rotation thereof, they produce a spin velocity in the air in the direction of rotation of said blades, means independent of the air moved by said fan for rotating said rotors in the direction of the movement of the air by the rotation of said blades, and means for adjusting said last mentioned means for varying the speed of rotation of said rotors for varying the volume of air moved by said fan.

4. In a fan having a plurality of air moving blades and an airl inlet, a plurality of rotors, means for so supporting said rotors in the path of the air enteringsvsaid inlet that upon rotation of same about their axes in the direction of the nair entering said inlet, a spin velocity in the direction of the rotation of said blades, is produced in the air entering said inlet, said means including shafts and shaft supporting means, said shaft supporting means being stationary, and means independent of the air passing through said inlet for rotating said rotors about their axes in the direction of the air entering said inlet, at variable speeds for varying said spin velocity, for varying the volume of air moved by said fan.

5. In a fan having a plurality of air moving blades and an air inlet, a plurality of rotors, means for so supporting said rotors in the path of the air entering said inlet with their axes converging that upon rotation of same about their axes in the direction of the air entering'said inlet, a spin velocity in the direction ofthe rotation of said blades, is produced in the air entering said inlet, said means including shafts and shaft supporting means, said shaft supporting means being stationary, and means Vindependent of the air passing through said inlet for y rotating said rotors about their axes in the direction of the air entering said inlet, at variablev speeds for varying said spin velocity, for varying the volume of air moved by said fan.

6. In a fan having a plurality of air moving blades and an axial air inlet, a plurality of rotors,

means for supporting said rotors with substantially parallel axes around said inlet, said means including shafts and shaft supporting means, said shaft supporting means being stationary, means for guiding the air entering said inlet in contact with said rotors, and means independent of the air entering said inlet, for rotating said rotors at variable speeds about their axes in the direction of the air entering said inlet, for producing variable spin velocities inthe air entering said inlet, for varying the volume of air moved by said fan.

JOHN E, MCDONALD. 

